Photo-patternable dielectric materials curable to porous dielectric materials, formulations, precursors and methods of use thereof

ABSTRACT

Silsesquioxane polymers that cure to porous silsesquioxane polymers, silsesquioxane polymers that cure to porous silsesquioxane polymers in negative tone photo-patternable dielectric formulations, methods of forming structures using negative tone photo-patternable dielectric formulations containing silsesquioxane polymers that cure to porous silsesquioxane polymers, structures containing porous silsesquioxane polymers and monomers and method of preparing monomers for silsesquioxane polymers that cure to porous silsesquioxane polymers.

RELATED APPLICATIONS

This Application is a division of U.S. patent application Ser. No.12/575,515 filed on Oct. 8, 2009, now U.S. Pat. No. 8,389,663, issuedMar. 5, 2013.

FIELD OF THE INVENTION

The present invention relates to the field of photo-patternable porousdielectric materials; more specifically, it relates to porouspatternable dielectric materials that become porous upon curing,photo-sensitive formulations containing patternable dielectric materialsthat become porous upon curing, methods of using photo-sensitiveformulations containing patternable dielectric materials that becomeporous upon curing in the fabrication of integrated circuits, integratedcircuit structures comprising porous dielectric materials and monomersand methods of preparing monomers for patternable dielectric materialsthat become porous upon curing.

BACKGROUND OF THE INVENTION

Integrated circuits include, for example, active devices such as fieldeffect transistors partially formed in a semiconductor substrate andinterconnected by wiring levels comprising wires formed in interleveldielectric layers formed on the substrate. Conventional wiring levelsare formed by depositing an interlevel dielectric layer, patterning aphotoresist layer formed on the dielectric layer, etching trenches inthe dielectric layer, removing the photoresist and filling the trencheswith metal. This is an expensive and time-consuming process.Accordingly, there exists a need in the art to mitigate the deficienciesand limitations described hereinabove.

SUMMARY OF THE INVENTION

A first aspect of the present invention is a composition of mattercomprising: a silsesquioxane polymer comprising (i) three monomers ofthe structural formulas (1), (2) and (3) or (ii) three monomers of thestructural formulas (1), (2) and (4) or (iii) four monomers of the ofthe structural formulas (1), (2), (3) and (4):

wherein R¹ is selected from the group consisting of linear alkyl,branched alkyl, cycloalkyl, aromatic, arene and ester moieties, eachcontaining 1 to 20 carbon atoms; wherein R² is an alkyl moietycontaining 1 to 20 carbon atoms; wherein R³ is selected from the groupconsisting of linear alkyl, branched alkyl and cycloalkyl moieties, eachcontaining 1 to 20 carbon atoms; and wherein m, n, o, and p representthe mole percent (mol %) of repeating units with m+n+o+p equal to orgreater than about 40 mol % and wherein when only three monomers arepresent either p is zero or o is zero.

A second aspect of the present invention is a photoactive formulation,comprising: a photoacid generator; a casting solvent; and asilsesquioxane polymer comprising (i) three monomers of the structuralformulas (1), (2) and (3) or (ii) three monomers of the structuralformulas (1), (2) and (4) or (iii) four monomers of the of thestructural formulas (1), (2), (3) and (4):

wherein R¹ is selected from the group consisting of linear alkyl,branched alkyl, cycloalkyl, aromatic, arene and ester moieties, eachcontaining 1 to 20 carbon atoms; wherein R² is an alkyl moietycontaining 1 to 20 carbon atoms; wherein R³ is selected from the groupconsisting of linear alkyl, branched alkyl and cycloalkyl moieties, eachcontaining 1 to 20 carbon atoms; and wherein m, n, o, and p representthe mole percent (mol %) of repeating units with m+n+o+p equal to orgreater than about 40 mol % and wherein when only three monomers arepresent either p is zero or o is zero.

A third aspect of the present invention is a method, comprising: (a)forming on a substrate, a layer of a photoactive formulation comprising:a photoacid generator; a casting solvent; and a silsesquioxane polymer;(b) patternwise exposing the layer with light to generate an exposedlayer; (c) baking the exposed layer to cross-link the silsesquioxanepolymer in regions of the exposed layer exposed to the light to generatea baked layer; (d) developing the baked layer to remove portions of thebaked layer not exposed to the light to form a first trench in adeveloped layer; (e) curing the developed layer to generate porosity inthe silsesquioxane polymer and form a porous patterned cured layerincluding the first trench; and (f) filling the first trench in theporous patterned cured layer with an electrically conductive material.

A fourth aspect of the present invention is a structure, comprising: across-linked layer of a porous silsesquioxane polymer on a substrate; atrench in said cross-linked layer; an electrically conductive materialfilling said trench and contacting said substrate in a bottom of saidtrench; and said porous silsesquioxane polymer comprising (i) threemonomers of the structural formulas (1), (7) and (4) or (ii) threemonomers of the structural formulas (1), (7) and (3) or (iii) fourmonomers of the structural formulas (1), (7), (3) and (4):

wherein R¹ is selected from the group consisting of linear alkyl,branched alkyl, cycloalkyl, aromatic, arene and ester moieties, eachcontaining 1 to 20 carbon atoms; wherein R³ is selected from the groupconsisting of linear alkyl, branched alkyl and cycloalkyl moieties, eachcontaining 1 to 20 carbon atoms; and wherein m, q, o, and p representthe mole percent (mol %) of repeating units with m+q+o+p equal to orgreater than about 40 mol % and wherein when only three monomers arepresent p is zero or o is zero.

A fifth aspect of the present invention is a composition of matterconsisting of:

wherein R⁵ is an alkyl moiety containing 1 to 20 carbon atoms and R⁶ isselected from the group consisting of halogens, alkanoates, amines, andalkoxides with the proviso that when R⁵ is methyl, R⁶ is not —Cl or—O—C₂H₅.

A sixth aspect of the present invention is a method of preparing anethylalkanoate silyl compound, wherein said compound comprises:

wherein R⁵ is an alkyl moiety containing 1 to 20 carbon atoms and R⁶ isselected from the group consisting of halogens, alkanoates, amines, andalkoxides; and

the method comprising:

-   -   adding a compound of the structure:

-   -   to a compound of the structure:

-   -   in the presence of a chloroplatinic acid.

These and other aspects of the invention are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention are set forth in the appended claims. Theinvention itself, however, will be best understood by reference to thefollowing detailed description of an illustrative embodiment when readin conjunction with the accompanying drawings, wherein:

FIGS. 1A through 1C illustrate steps in a method of forming single ordual-damascene wires using a photo-patternable dielectric materialaccording to embodiments of the present invention;

FIGS. 2A and 2B illustrate steps in a method of forming single damascenewires in a photo-patternable dielectric material according toembodiments of the present invention;

FIGS. 3A through 3E illustrate steps in a method of formingdual-damascene wires in a photo-patternable dielectric materialaccording to embodiments of the present invention; and

FIG. 4 is a flowchart describing a method of forming single- and dualdamascene wires in dielectric material formed using a negative tonephoto-patternable dielectric formulation according to embodiments of thepresent invention.

DETAILED DESCRIPTION

The present invention describes silsesquioxane polymers that may bemixed with one or more photoacid generators, an optional casting solventand one or more optional additives to form a negative tonephoto-patternable dielectric formulation that becomes porous uponcuring. The silsesquioxane polymers of embodiments of the presentinvention may be linear polymers, branched polymers, caged polymers orcombinations of thereof. The silsesquioxane polymers of embodiments ofthe present invention are preferably aqueous base soluble. Patternwiseexposure of a layer of the formulation directly forms a cross-linkedpatterned dielectric layer (without the use of photoresist basedlithography or etching of the dielectric layer) after development. Aftercuring the patterned dielectric layer, a porous low dielectric constant(k) patterned dielectric layer is produced. A low-k material is definedas a material having a dielectric constant of about 3.0 or less.

The silsesquioxane polymers of the present invention preferably containsilanol endgroups with silyl ethers and silyl alcohols preferred (andmay contain monomers having silanol moieties with silyl ethers and silylalcohols preferred) which undergo cross-linking via condensation in thepresence of acid released by the photoacid generator after exposure tolight (heat increases the efficiency of the reaction). Thesilsesquioxane polymers according to embodiments of the presentinvention may also include halosilane, acetoxysilane, silylamine, andalkoxysilane endgroups depending upon the functional endgroups of themonomers used in the polymerization reaction. Cross-linking enables theformation of chemical bonds, which can withstand standard thermal curingand subsequent curing conditions such as ultraviolet (UV)-thermaltreatment.

Moreover, the silsesquioxane polymers according to embodiments of thepresent invention contain an ethylalkanoate side-chain functionality,which undergoes a partial decomposition reaction during curing togenerate a porous low-k insulating material (k less than about 3).Further, the inventors have found that incorporating an ethyl alkanoatesilsesquioxane monomers into polymers allows for higher amounts ofbis-triethoxysilylethane (BTSE) monomer to be incorporated intosilsesquioxane polymers containing BTSE monomers. This unexpected resultallows the formation of polymers with improved mechanical properties.

The silsesquioxane polymers of the present invention are particularlyuseful in forming damascene and dual-damascene wires without the use ofa photoresist since they can be patterned directly.

A damascene process is one in which a dielectric layer having wiretrenches or via openings extending through a dielectric layer is formed,an electrical conductor of sufficient thickness to fill the trenches isdeposited in the trenches and on a top surface of the dielectric, and achemical-mechanical-polish (CMP) process is performed to remove excessconductor and make the surface of the conductor co-planar with thesurface of the dielectric layer to form damascene wires (or damascenevias). When only a trench and a wire (or a via opening and a via) areformed the process is called single-damascene.

A via-first dual-damascene process (according to embodiments of thepresent invention) is one in which a first dielectric layer having viaopenings extending through the first dielectric layer are formedfollowed by formation of a second dielectric layer having trenchesextending through the second dielectric layer and intersecting thetrenches in the first dielectric layer. All via openings are intersectedby integral wire trenches above, but not all trenches need intersect avia opening. An electrical conductor of sufficient thickness to fill thetrenches and via openings is deposited on a top surface of thedielectric. A CMP process is performed to make the surface of theconductor in the trench co-planar with the surface of the dielectriclayer to form dual-damascene wires and dual-damascene wires havingintegral dual-damascene vias.

In one example, silsesquioxane polymers of the embodiments of thepresent invention comprise (i) three monomers of the structural formulas(1), (2) and (3) or (ii) three monomers of the structural formulas (1),(2) and (4) or (iii) four monomers of the structural formulas (1), (2),(3) and (4):

wherein R¹ is selected from the group consisting of linear alkyl,branched alkyl, cycloalkyl, aromatic, arene and ester moieties, eachcontaining 1 to 20 carbon atoms; R² is an alkyl moiety containing 1 to20 carbon atoms; and R³ is selected from the group consisting of linearalkyl, branched alkyl and cycloalkyl moieties, each containing 1 to 20carbon atoms; and m, n, o, and p represent the mole percent (mol %) ofrepeating units. When only three monomers are present either p is zeroor o is zero.

Mol % is mole-fraction times 100. 10 mol % is thus 0.1 mol fraction ofthe polymer.

Preferred R¹ moieties are selected from the group consisting of methyl,ethyl, propyl, isopropyl, cyclohexyl, and norbornyl groups. Preferred R²moieties are selected from the group consisting of methyl, ethyl,propyl, n-alkyl (CH₃—(CH₂)_(x)— where x is 0 to 20), isopropyl,tert-butyl, 2,2 dimethylheptyl, cyclohexyl and norbornyl groups. Apreferred R³ moiety is an ethyl group.

In silsesquioxane polymers according to embodiments of the presentinvention, R¹ is a carbon containing group for controlling polymerdissolution in aqueous base; R² is the alkyl group of the ethylalkanoate for generating porosity during curing; R³ is a C₁-C₂₀hydrocarbon moiety and structural formula (3) is a bridge.

In one example, silsesquioxane polymers according to embodiments of thepresent invention comprise monomers of structural formulas (1), (2), (3)and (4) with m+n+o+p equal or greater than about 40 mol %, with equal toor greater than about 75% preferred, with equal to or greater than about95% more preferred, and with equal to or greater than about 99% stillmore preferred.

In one example, silsesquioxane polymers according to embodiments of thepresent invention, m is between about 10 mol % and about 90 mol %, n isbetween 1 mol % and about 90 mol %, o is between about 0 mol % and about10 mol % and p is between about 0 mol % and about 60 mol % of the finalpolymer composition, where 0 mol % indicates the monomer is not presentin the polymer. In one example, silsesquioxane polymers according toembodiments of the present invention, m is between about 50 mol % andabout 80 mol %, n is between 5 mol % and about 40 mol %, o is betweenabout 0 mol % and about 40 mol % and p is between about 1 mol % andabout 60 mol % of the final polymer composition, where 0 mol % indicatesthe monomer is not present in the polymer. Both o and p are notsimultaneously 0 mol % for a given polymer composition.

In one example, silsesquioxane polymers of embodiments of the presentinvention consist essentially of (i) three monomers of the structuralformulas (1), (2) and (3) or (ii) three monomers of the structuralformulas (1), (2) and (4) or (iii) four monomers of the structuralformulas (1), (2), (3) and (4):

wherein R¹ is selected from the group consisting of linear alkyl,branched alkyl, cycloalkyl, aromatic, arene and ester moieties, eachcontaining 1 to 20 carbon atoms; R² is an alkyl moiety containing 1 to20 carbon atoms; and R³ is selected from the group consisting of linearalkyl, branched alkyl and cycloalkyl moieties, each containing 1 to 20carbon atoms; and m+n+o+p is equal to about 100 mol %. When only threemonomers are present either p is zero or o is zero.

A preferred first silsesquioxane polymer consists essentially ofmonomers of structural formulas (1), (2), (3) and (4), R¹ is a methylmoiety and m is between about 40 mol % and about 70 mol %, R² is amethyl moiety and n is between about 5 mol % and about 15 mol %, R³ isan ethyl moiety and o is between about 10 mol % and about 30 mol %, andp is between about 5 mol % and about 15 mol %.

A preferred second silsesquioxane polymer consists essentially ofmonomers of structural formulas (1), (2), (3) and (4), R¹ is a methylmoiety and m is between about 40 mol % and about 70 mol %, R² is antert-butyl moiety and n is between about 5 mol % and about 15 mol %, R³is an ethyl moiety and o is between about 10 mol % and about 30 mol %,and p is between about 5 mol % and about 15 mol %.

A preferred third silsesquioxane polymer, consists essentially ofmonomers of structural formulas (1), (2), (3) and (4), R¹ is a methylmoiety and m is between about 40 mol % and about 70 mol %, R² is anneodecanyl moiety and n is between about 5 mol % and about 15 mol %, R³is an ethyl moiety and o is between about 10 mol % and 30 mol %, and pis between about 5 mol % and about 15 mol %.

In one example, the silsesquioxane polymers of the embodiments of thepresent invention have a weight-averaged molecular weight between about400 Daltons and about 500,000 Daltons. In one example, thesilsesquioxane polymers of the embodiments of the present invention havea weight-averaged molecular weight between about 1,500 Daltons and about20,000 Daltons.

Negative tone photo-patternable dielectric formulations according toembodiments of the present invention include the silsesquioxane polymersof combinations of monomers (1), (2), (3) and (4) discussed supra, aphotoacid generator (PAG), and a casting solvent. Negative tonephoto-patternable dielectric formulations according to embodiments ofthe present invention may optionally include one or more additives suchas organic bases, cross-linking agents and additive polymers.

Examples of PAGs include, but are not limited to, triphenylsulfoniumnonaflate,co(trifluoro-methylsulfonyloxy)-bicyclo[2.2.1]hept-5-ene-2,3-dicarboximide(MDT), N-hydroxy-naphthalimide (DDSN), onium salts, aromatic diazoniumsalts, sulfonium salts, diaryliodonium salts, and sulfonic acid estersof N-hydroxyamides, imides, or combinations thereof.

Examples of casting solvents include, but are not limited to,ethoxyethylpropionate (EEP), a combination of EEP and γ-butyrolactone,propylene-glycol monomethylether acetate (PGMEA) propylene-glycolmonomethylether alcohol, propyleneglycol monopropyl alcohol,propyleneglycol monopropyl acetate, ethyl lactate, or combinationsthereof.

The organic base may be any suitable organic base known in thephotoresist art. Examples of organic bases include, but are not limitedto, tetraalkylammonium hydroxides, cetyltrimethylammonium hydroxide,1,8-diaminonaphthalene and combinations thereof. The negative tonephoto-patternable dielectric formulations of the embodiments of thepresent invention are not limited to any specific selection of organicbase.

Examples of cross-linking agents include, but are not limited to,methylphenyltetramethoxymethyl glycouril (methylphenyl POWDERLINK),tetramethoxymethyl glycouril, methylpropyltetramethoxymethyl glycouril,and 2,6-bis(hydroxymethyl)-p-cresol.

An example of a polymer additive is the silsesquioxanes polymer havingthe structural formula:

wherein R⁴ is selected from the group consisting of alkyl, cycloalkyland aryl moieties and s is an integer between about 10 and about 1000.Many polymers of structural formula (5) are commercially available, forexample, from Dow Corning, Shin-Etsu, or JSR Corporation.

In one example, the silsesquioxane polymer additive possesses silanolend groups, but may also include halosilane, acetoxysilane, silylamine,and alkoxysilane endgroups. In a preferred embodiment of the presentinvention the additive polymer is a silsesquioxane polymer LKD-2015 (JSRCorporation) that contains silanol end groups.

The additive polymer comprises between about 1% by weight to about 99%by weight of all polymers of the negative tone photo-patternabledielectric formulations, with between about 20% by weight and 80% byweight preferred, and between about 30% by weight and 60% by weight morepreferred.

The monomer of structure (2) may be synthesized by a hydrosilationreaction between a hydridosilane and a vinyl ester:

In one example, R⁵ is an alkyl moiety containing 1 to 20 carbon atomsand R⁶ is selected from the group of halogens, alkanoates, amines, andalkoxides. In one example, R⁵ is an alkyl moiety containing 1 to 20carbon atoms and R⁶ is selected from the group of halogens, alkanoates,amines, and alkoxides with the proviso that when R⁵ is methyl, R⁶ is not—Cl or —O—C₂H₅. In one example R5 is methyl, tert-butyl or neodecanyl.In one example, the Pt catalyst is chloroplatinic acid.

FIGS. 1A through 1C illustrate steps in a method of forming single ordual-damascene wires using a photo-patternable dielectric materialaccording to embodiments of the present invention. In FIG. 1A, aphoto-patternable dielectric layer 105 is formed on a substrate 100.Photo-patternable dielectric layer 105 is formed by spin coating,spraying or dip coating substrate 100 with a negative tonephoto-patternable dielectric formulation according to embodiments of thepresent invention described supra. If a negative tone photo-patternabledielectric formulation includes an optional casting solvent, afterapplying the negative tone photo-patternable dielectric formulation apre-exposure bake (at a temperature between about 80° C. and about 120°C. with about 110° C. preferred) is performed to drive out the castingsolvent and form photo-patternable dielectric layer 105. In one example,substrate 100 includes devices such as field effect transistors, bipolartransistors, diodes, resistors, capacitors and inductors as well ascontacts and damascene and/or dual-damascene wires (which wires may beformed using embodiments of the present invention or conventionalprocesses).

In FIG. 1B, photo-patternable dielectric layer 105 is patternwiseexposed to light through a mask 110. Mask 110 comprises a transparent orsemi-transparent (to the wavelength of the light being used) substrate115 having an opaque or semi-opaque to the wavelength of the light beingused) image 120. More light passes through substrate 115 than throughthe combination of substrate 115 and image 120. One image 120 isillustrated, but there are typically hundreds of thousands to millionsof such images present on a mask used to form integrated circuits. Uponexposure to the light, a pattern of unexposed regions 125 and exposedregions 130 is formed in photo-patternable dielectric layer 105. Lightincludes ultraviolet (UV) light (between about 10 nm and about 400 nm)and extreme UV light (between about 10 nm and about 13.5 nm). Electronbeam irradiation may be used instead of UV or extreme UV light. In oneexample, the light has a wavelength of about 248 nm. In one example, thelight has a wavelength of about 193 nm. In one example, the light has awavelength of about 157 nm.

In FIG. 1C, a post exposure bake followed by a develop process followedby a curing process is performed to form a porous (and low k) patterneddielectric layer 135 having an opening 140 therein. A top surface 142 ofsubstrate 140 is exposed in the bottom of opening 140. In one example,the post-exposure bake is performed at a temperature between about 35°C. and about 200° C. with a temperature between about 80° C. and about120° C. preferred. The patternwise light (or electron beam) exposurecauses the photoacid generator(s) in photo-patternable dielectric layer105 (see FIG. 1B) to generate acid which cross-links the polymer throughthe hydroxyl, alkoxy, silyloxy or silanol endgroups in regions 130 (seeFIG. 1B) making the polymer insoluble in basic developer. The postexposure bake enhances this cross-linking process. Suitable developersinclude organic or aqueous bases with aqueous basic developerspreferred. In one example the developer is an aqueous solution oftetramethylammonium hydroxide. In one example, the curing process is abake at a temperature of about 100° C. or higher. In one example, thecuring process is a bake at a temperature of about 250° C. or higher. Inone example, the curing process is a UV exposure using light of awavelength between about 50 nm and about 300 nm. In one example, thecuring process includes simultaneous exposure to UV light at awavelength between about 50 nm and about 300 nm and heating to about100° C. or higher. In one example, the curing process includessimultaneous exposure to UV light at a wavelength between about 50 nmand about 300 nm and heating to about 250° C. or higher.

The curing process causes the loss of the ethylalkanoate group ofstructure (2) via decomposition of the ethylalkanoate to releaseethylene and an organic acid, while simultaneously generating structure7.

The inventors unexpectedly found that curing a dielectric layercontaining a silsesquioxane polymer having structure (2) or (6) forms aporous dielectric film. The dielectric constant (k) is less than 3.0. Inone example, the dielectric constant of the film is less than 2.5.

Thus, after curing the now porous silsesquioxane polymer comprises (i)three monomers of the structural formulas (1), (7) and (4) or (ii) threemonomers of the structural formulas (1), (7) and (3) or (iii) fourmonomers of the structural formulas (1), (7), (3) and (4):

wherein R¹ is selected from the group consisting of linear alkyl,branched alkyl, cycloalkyl, aromatic, arene and ester moieties, eachcontaining 1 to 20 carbon atoms; wherein R³ is selected from the groupconsisting of linear alkyl, branched alkyl and cycloalkyl moieties, eachcontaining 1 to 20 carbon atoms; and wherein m, q, o, and p representthe mole percent (mol %) of repeating units with m+q+o+p equal to orgreater than about 40 mol %, with equal to or greater than about 75%preferred, with equal to or greater than about 95% more preferred, andwith equal to or greater than about 99% still more preferred and whereinwhen only three monomers are present either p is zero or o is zero.

In one example, porous silsesquioxane polymers according to embodimentsof the present invention, m is between about 10 mol % and about 90 mol%, q is between 1 mol % and about 90 mol %, o is between about 0 mol %and about 10 mol % and p is between about 0 mol % and about 60 mol % ofthe cured polymer, where 0 mol % indicates the monomer is not present inthe polymer. In one example, porous silsesquioxane polymers according toembodiments of the present invention, m is between about 50 mol % andabout 80 mol %, q is between 5 mol % and about 40 mol %, o is betweenabout 0 mol % and about 40 mol % and p is between about 1 mol % andabout 60 mol % of the cured polymer, where 0 mol % indicates the monomeris not present in the polymer.

In one example, the porous silsesquioxane polymers of embodiments of thepresent invention consist essentially of (i) three monomers of thestructural formulas (1), (7) and (3) or (ii) three monomers of thestructural formulas (1), (7) and (4) or (iii) four monomers of thestructural formulas (1), (7), (3) and (4):

wherein R¹ is selected from the group consisting of linear alkyl,branched alkyl, cycloalkyl, aromatic, arene and ester moieties, eachcontaining 1 to 20 carbon atoms; R³ is selected from the groupconsisting of linear alkyl, branched alkyl and cycloalkyl moieties, eachcontaining 1 to 20 carbon atoms; and m+q+o+p is equal to about 100 mol%. When structure (4) is not present p is 0. When structure (3) is notpresent, o is zero.

A preferred porous silsesquioxane polymer, consists essentially ofmonomers of structural formulas (1), (7), (3) and (4), R¹ is a methylmoiety and m is between about 40 mol % and about 70 mol %, q is betweenabout 5 mol % and about 15 mol %, and R³ is an ethyl moiety and o isbetween about 10 mol % and about 30 mol %, and p is between about 5 mol% and about 15 mol %.

FIGS. 2A and 2B illustrate steps in a method of forming single damascenewires in a photo-patternable dielectric material according toembodiments of the present invention. FIG. 2A continues from FIG. 1C.

In FIG. 2A, a layer 145 of electrically conductive material is formed onthe top surface of patterned dielectric layer 135 and the top surface142 of substrate 100 exposed in opening 140. Layer 145 completely fillsopening 140. In one example, layer 145 comprises one or more layers ofmetal. In one example, layer 145 comprises a conformal layer of tantalumnitride in contact with patterned dielectric layer 135 (including thesidewalls of opening 140) and substrate 100, a conformal layer oftantalum on the tantalum nitride layer, and a copper layer (i.e., core)on the tantalum layer.

In FIG. 2B, planarization process (e.g., a chemical-mechanical-polish(CMP)) is performed so a top surface 147 of patterned dielectric layer135 is coplanar with a top surface 148 of single-damascene wire (orcontact) 150. Wire 150 may electrically contact a device (e.g., a gateelectrode of an FET) or another wire of a lower wiring level insubstrate 100.

FIGS. 3A through 3C illustrate steps in a method of formingdual-damascene wires in a photo-patternable dielectric materialaccording to embodiments of the present invention. FIG. 3A continuesfrom FIG. 1C.

In FIG. 3A, a photo-patternable dielectric layer 155 is formed on apatterned dielectric layer 135 filling opening 140. Photo-patternabledielectric layer 155 is formed by spin coating, spraying or dip coatingsubstrate 100 with a negative tone photo-patternable dielectricformulation according to embodiments of the present invention describedsupra. If a negative tone photo-patternable dielectric formulationincludes a optional casting solvent, after applying the negative tonephoto-patternable dielectric formulation a pre-exposure bake (e.g., at atemperature between about 80° C. and about 120° C. with about 110° C.preferred) is performed to drive out the casting solvent and formphoto-patternable dielectric layer 155.

In FIG. 3B, photo-patternable dielectric layer 155 is patternwiseexposed to light through a mask 160. Mask 160 comprises a transparent orsemi-transparent (to the wavelength of the light being used) substrate165 having an opaque or semi-opaque (to the wavelength of the lightbeing used) image 160. More light passes through substrate 165 thanthrough the combination of substrate 165 and image 170. One image 160 isillustrated, but there are typically hundreds of thousands to millionsof such images present on a mask used to form integrated circuits. Uponexposure to the light, a pattern of unexposed regions 175A and exposedregions 175B is formed in photo-patternable dielectric layer 155.

In FIG. 3C, a post exposure bake followed by a develop process followedby a curing process is performed to form a porous patterned dielectriclayer 180 having an opening 185 therein. Opening 140 in patterneddielectric layer 135 is exposed in the bottom of opening 185. Opening140 has a width W1 and opening 185 has a width W2 with W2>W1. In oneexample, the post-exposure bake is performed at a temperature betweenabout 35° C. and about 200° C., with a temperature between about 80° C.and about 120° C. preferred. The patternwise exposure to light causesthe photoacid generator(s) in photo-patternable dielectric layer 155(see FIG. 3B) to generate acid which cross-links the polymer through thehydroxyl, alkoxy, silyloxy or silanol endgroups in regions 175B (seeFIG. 3B) making the polymer insoluble in basic developer. The postexposure bake enhances this cross-linking process. In one example, thecuring process is a bake at a temperature of about 100° C. or higher. Inone example, the curing process is a bake at a temperature of about 250°C. or higher. In one example, the curing process is a UV exposure usinglight of a wavelength between about 50 nm and about 300 nm. In oneexample, the curing process includes simultaneous exposure to UV lightat a wavelength between about 50 nm and about 300 nm and heating toabout 100° C. or higher. In one example, the curing process includessimultaneous exposure to UV light at a wavelength between about 50 nmand about 300 nm and heating to about 250° C. or higher. Again, the lossof the ethylalkonate group generates the porosity in a porous patterneddielectric layer 180.

In FIG. 3D, a layer 190 of electrically conductive material is formed onthe top surface of patterned dielectric layer 180, exposed surfaces ofpatterned dielectric layer 135, and the top surface 142 of substrate 100exposed in opening 140. Layer 190 completely fills openings 140 and 185.In one example, layer 190 comprises one or more layers of metal. In oneexample, layer 190 comprises a conformal layer of tantalum nitride incontact with patterned dielectric layers 135 and 180 (including thesidewalls of openings 140 and 180 and the top surface of patterneddielectric that was exposed in opening 185 in FIG. 3C) and substrate100, a conformal layer of tantalum on the tantalum nitride layer, and acopper layer (i.e., core) on the tantalum layer.

In FIG. 3E, a planarization process (e.g., a CMP) is performed so a topsurface 187 of patterned dielectric layer 180 is coplanar with a topsurface 188 of a dual-damascene wire 195. Wire 195 may electricallycontact another wire of a lower wiring level in substrate 100.

FIG. 4 is a flowchart describing a method of forming single- and dualdamascene wires in dielectric material formed using a negative tonephoto-patternable dielectric formulation according to embodiments of thepresent invention. In step 200, a negative tone photo-patternabledielectric formulation according to embodiments of the present inventionis applied to form a photo-patternable dielectric layer on a substrate(e.g., an integrated circuit undergoing fabrication) as illustrated inFIG. 1A and described supra. In step 205, the photo-patternabledielectric layer is patternwise exposed as illustrated in FIG. 1B anddescribed supra. In step 210, a post exposure bake is performed, in step215 the exposed photo-patternable dielectric layer is developed, and instep 220, the developed photo-patternable dielectric layer is cured toform a patterned dielectric layer as illustrated in FIG. 1C anddescribed supra.

In step 225, it is decided if the wire to be formed is to be asingle-damascene wire or a dual-damascene wire. If a single-damascenewire is to be formed the method proceeds to step 230.

In step 230, an electrically conductive layer as illustrated in FIG. 2Aand described supra is formed and in step 235 a planarization process asillustrated in FIG. 2B and described supra is performed to completefabrication of a single-damascene wire.

Returning to step 225, if a dual-damascene wire is to be formed themethod proceeds to step 240. In step 240, a negative tonephoto-patternable dielectric formulation according to embodiments of thepresent invention is applied to form a photo-patternable dielectriclayer on a substrate (e.g., an integrated circuit undergoingfabrication) as illustrated in FIG. 3A and described supra. In step 245,the photo-patternable dielectric layer is patternwise exposed asillustrated in FIG. 3B and described supra. In step 250, a post exposurebake is performed, in step 255 the exposed photo-patternable dielectriclayer is developed, and in step 260, the developed photo-patternabledielectric layer is cured to form a patterned dielectric layer asillustrated in FIG. 3C and described supra. In step 265, an electricallyconductive layer as illustrated in FIG. 3D and described supra is formedand in step 270 a planarization process as illustrated in FIG. 3E anddescribed supra is performed to complete fabrication of a dual-damascenewire.

EXAMPLES

The following examples provide further description of the presentinvention. The invention is not limited to the details of the examples.Where appropriate, the following techniques and equipment were utilizedin the Examples: ¹H and ¹³C NMR spectra were obtained at roomtemperature on an Avance 400 spectrometer. Quantitative ¹³C NMR was runat room temperature in acetone-d₆ in an inverse-gated ¹H-decoupled modeusing Cr(acac)₃ as a relaxation agent on an Avance 400 spectrometer.Thermo-gravimetric analysis (TGA) was performed at a heating rate of 5°C./min in N₂ on a TA Instrument Hi-Res TGA 2950 ThermogravimetricAnalyzer. Differential scanning calorimetry (DSC) was performed at aheating rate of 10° C./min on a TA Instruments DSC 2920 modulateddifferential scanning calorimeter. Molecular weights were measured intetrahydrofuran (THF) on a Waters Model 150 chromatograph relative topolystyrene standards. IR spectra were recorded on a Nicolet 510 FT-IRspectrometer on a film cast on a KBr plate. Film thickness was measuredon a Tencor alpha-step 2000. A quartz crystal microbalance (QCM) wasused to study the dissolution kinetics of the resist films in an aqueoustetramethylammonium hydroxide (TMAH) solution (CD-26).

When polymers according to embodiments of the present invention aresynthesized using triethoxymethylsilane, the monomer of structuralformula (1) is generated with R¹ being —CH₃, the monomer may be calledmethylsilsesquioxane. When polymers according to embodiments of thepresent invention are synthesized using acetoxyethyltriethoxylsilane,the monomer of structural formula (2) is generated with R² being —CH₃,the monomer may be called acetoxyethyltriethoxysilsesquioxane. Whenpolymers according to embodiments of the present invention aresynthesized using 2-(triethoxysilyl)ethyl pivalate, the monomer ofstructural formula (2) is generated with R² being —C(CH₃)₃, the monomermay be called pivalatoxyethylsilsesquioxane. When polymers according toembodiments of the present invention are synthesized using2-(triethoxysilyl)ethyl neodecanote, the monomer of structural formula(2) is generated with R² being —C₉H₁₉, the monomer may be calledneodecanotoxyethylsilsesquioxane. When terpolymers and quadpolymersaccording to embodiments of the present invention are synthesized usingbis-(triethoxysilyl)ethane, the monomer of structural formula (3) isgenerated with R³ being —CH₂—CH₂— and the monomer may be calledbis-(silsequioxyl)ethane. When terpolymers and quadpolymers according toembodiments of the present invention are synthesized usingtetraethoxysilane, the monomer of structural formula (4), the monomermay be called tetraethoxysilane.

Example 1 Synthesis of Aetoxyethyltriethoxysilane

A 250 milliliter (ml) two-necked round-bottom flask equipped with adropping funnel, magnetic stirrer, and condenser with nitrogen inlet wascharged with chloroplatinic(IV) acid hexahydrate (0.1 g, 0.193×10⁻³mole) and triethoxysilane (50 g, 0.30 mole). The mixture was heated at80° C. with stirring under nitrogen until the solution turned black (˜15minutes). At this juncture, the heating to the reaction mixture wasdiscontinued and vinyl acetate (43 g, 0.5 mole) was added dropwise tothe reaction mixture. The dropwise addition of vinyl acetate led to aexothermic self-sustaining hydrosilylation reaction. After the additionof vinyl acetate, the solution was stirred at room temperature for 2hours. The product acetoxyethyltriethoxysilane was fractionallydistilled from the solution at reduced pressure. Yield ˜95%.

Example 2 Synthesis of Pivalatoxyethyltriethoxysilane

A 250 ml two-necked round-bottom flask equipped with a dropping funnel,magnetic stirrer, and a condenser with nitrogen inlet was charged withchloroplatinic(IV) acid hexahydrate (0.1 g, 0.193×10⁻³ mole) andtriethoxysilane (50 g, 0.30 mole). The mixture was heated at 80° C. withstirring under nitrogen until the mixture turned black (˜15 minutes). Atthis juncture, the heating to the reaction mixture was discontinued andvinyl pivalate (38.9 g, 0.30 mole) was added dropwise to the reactionmixture. The dropwise addition of vinyl pivalate led to a exothermicself-sustaining hydrosilylation reaction. After the addition of vinylpivalate, the solution was stirred at room temperature for 2 hours. Theproduct pivalatoxyethyltriethoxysilane was fractionally distilled fromthe solution at reduced pressure. Yield ˜95%.

Example 3 Synthesis of Neodecanotoxyethyltriethoxysilane

A 250 mL two-necked round-bottom flask equipped with a dropping funnel,magnetic stirrer, and condenser with nitrogen inlet was charged withchloroplatinic(IV) acid hexahydrate (0.1 g, 0.193×10⁻³ mole) andtriethoxysilane (50 g, 0.30 mole). The mixture was heated at 80° C. withstirring under nitrogen until the mixture turned black (˜15 minutes). Atthis juncture, the heating to the reaction mixture was discontinued andvinyl neodecanoate (60 g, 0.30 mole) was added dropwise to the reactionmixture. The dropwise addition of vinyl neodecanoate led to a exothermicself-sustaining hydrosilylation reaction. After the addition of vinylneodecanoate, the solution was stirred at room temperature for 2 hours.The mixture was then stirred overnight with activated charcoal (0.2 g)and the product neodecanotoxyethyltriethoxysilane was recovered byfiltering the solution. Yield ˜95%.

Example 4 Synthesis ofPoly[methylsilsesquioxane-co-acetoxyethylsilsesquioxane-co-bis-silsesquioxylethane-co-tetraethoxysilane]

A 250 milliliter (ml) three neck round-bottom flask equipped with athermocouple thermometer, magnetic stirrer, condenser with nitrogeninlet, and a temperature controlled heating mantle was charged with amixture of triethoxymethylsilane (39.23 grams, 0.22 mole),acetoxyethyltriethoxysilane (10.01 g, 0.04 mole), tetraethoxysilane(8.33 grams, 0.04 mole), bis(triethoxysilyl)ethane (28.36 g, 0.08moles), and 67.5 grams of methyl isobutyl ketone. The mixture was heatedwith stirring under nitrogen and 25.2 ml of a 1.75 wt % solution ofoxalic acid in water was added to the above mixture at 50° C. Thereaction mixture was initially inhomogeneous, but after 15 minutes ofstirring became homogeneous. The homogenization of the reaction mixturewas accompanied by the exothermic reaction leading to increase intemperature to around 80° C. The temperature was brought down to 50° C.and the mixture was stirred for a total of 5 hours. Thereafter, themixture was cooled to room temperature and diluted with 150 ml of ethylacetate. This mixture was extracted with eight 100 ml portions ofdeionized water (final water extract was almost neutral to pH paper).The organic layer was evaporated to yield 24.0 grams of hard foam afterevacuation at high vacuum and room temperature for 24 hours. The molarratio of monomers (1), (2), (3) and (4) was 11:2:4:2.

Example 5 Synthesis ofPoly[methylsilsesquioxane-co-pivalatoxyethylsilsesquioxane-co-bis-(silsesquioxyl)ethane-co-tetraethoxysilane]

A 250 ml three neck round-bottom flask equipped with a thermocouplethermometer, magnetic stirrer, condenser with nitrogen inlet, and atemperature controlled heating mantle was charged with a mixture oftriethoxymethylsilane (39.23 grams, 0.22 mole), 2-(triethoxysilyl)ethylpivalate (11.68 g, 0.04 mole), tetraethoxysilane (8.33 grams, 0.04mole), bis(triethoxysilyl)ethane (28.36 g, 0.08 mole), and 67.5 grams ofmethyl isobutyl ketone. The mixture was heated with stirring undernitrogen and 25.2 ml of a 1.75 wt % solution of oxalic acid in water wasadded to the above mixture at 50° C. The reaction mixture was initiallyinhomogeneous, but after 15 minutes of stirring became homogeneous. Thehomogenization of the reaction mixture was accompanied by the exothermicreaction leading to an increase in temperature to around 80° C. Thetemperature was brought down to 50° C. and the mixture was stirred for atotal of 5 hours. Thereafter, the mixture was cooled to room temperatureand diluted with 150 ml of ethyl acetate. This mixture was extractedwith eight 100 ml portions of deionized water (final water extract wasalmost neutral to pH paper). The organic layer was evaporated to yield23.2 grams of hard foam after evacuation at high vacuum and roomtemperature for 24 hours. The molar ratio of monomers (1), (2), (3) and(4) was 11:2:4:2.

Example 6 Synthesis ofPoly[methylsilsesquioxane-co-neodecanotoethylsilsesquioxane-co-bis-(silsesquioxyl)ethane-co-tetraethoxysilane]

A 250 ml three neck round-bottom flask equipped with a thermocouplethermometer, magnetic stirrer, condenser with nitrogen inlet, and atemperature controlled heating mantle was charged with a mixture oftriethoxymethylsilane (39.23 grams, 0.22 mole), 2-(triethoxysilyl)ethylneodecanoate (14.48 g, 0.04 mole), tetraethoxysilane (8.33 grams, 0.04moles), bis(triethoxysilyl)ethane (28.36 g, 0.08 moles), and 67.5 gramsof methyl isobutyl ketone. The mixture was heated with stirring undernitrogen and 25.2 ml of a 1.75 wt % solution of oxalic acid in water wasadded to the above mixture at 50° C. The reaction mixture was initiallyinhomogeneous, but after 15 minutes of stirring became homogeneous. Thehomogenization of the reaction mixture was accompanied by the exothermicreaction leading to increase in temperature to around 80° C. Thetemperature was brought down to 50° C. and the mixture was stirred for atotal of 5 hours. Thereafter, the mixture was cooled to room temperatureand diluted with 150 ml of ethyl acetate. This mixture was extractedwith eight 100 ml portions of deionized water (final water extract wasalmost neutral to pH paper). The organic layer was evaporated to yield21.7 grams of hard foam after evacuation at high vacuum and roomtemperature for 24 hours. The molar ratio of monomers (1), (2), (3) and(4) was 11:2:4:2.

Example 7 Synthesis ofPoly[Methylsilsesquioxane-co-Neodecanotoxyethylsilsesquioxane-co-Tetraethoxysilane-co-Bis-(silsesquioxyl)ethane]9:5:2:5

A 250 ml three neck round-bottom flask equipped with a thermocouplethermometer, magnetic stirrer, condenser with nitrogen inlet, and atemperature controlled heating mantle was charged with a mixture oftriethoxymethylsilane (16.05 grams, 0.09 moles), 2-(triethoxysilyl)ethylneodecanoate (18.1 g, 0.05 mole), tetraethoxysilane (4.16 grams, 0.02moles), bis(triethoxysilyl)ethane (17.73 g, 0.05 moles), and 50 grams ofmethyl isobutyl ketone. The mixture was heated with stirring undernitrogen and 12 ml of a 1.75 wt % solution of oxalic acid in water wasadded to the above mixture at 50° C. The reaction mixture was initiallyinhomogeneous, but after 15 minutes of stirring became homogeneous. Thehomogenization of the reaction mixture was accompanied by the exothermicreaction leading to increase in temperature to around 70° C. Thetemperature was brought down to 50° C. and the mixture was stirred for atotal of 5 hours. Thereafter, the mixture was cooled to room temperatureand diluted with 100 ml of ethyl acetate. This mixture was extractedwith eight 100 ml portions of deionized water (final water extract wasalmost neutral to pH paper). The organic layer was evaporated to yield15 grams of hard foam after evacuation at high vacuum and roomtemperature for 24 hours.

Example 8 Dielectric Constant

Dielectric constants were measured for cured samples of each of thepolymers of examples 1, 2 and 3. Films of the polymers were spin appliedonto silicon wafers and then post-applied baked at 110° C. for 1 min,exposed to 248 nm light, post-exposure baked at 110° C. for 1 min, andthen thermally cured at 400° C. The dielectric constant for the polymersdescribed in examples 4, 6 and 7 was 2.88, 2.86, and 2.80 respectively.

Example 9 Photo-patternable Composition

A patternable low-k composition was formulated with 16.5 wt % solutionof

Poly[methylsilsesquioxane-co-acetoxyethylsilsesquioxane-co-bis-(silsesquioxyl)ethane-co-tetraethoxysilane]and 2 wt % of triphenylsulfonium nonaflate in PGMEA, and 0.6 parts of anorganic base. The resulting low-k formulation was filtered through a 0.2μm filter. The low-k composition was spin coated onto an 8 inch siliconwafer and pre-exposure baked at 110° C. for 60 s, patternwise exposed to248 nm UV light on an ASML (0.63 NA, ⅝ annular) DUV stepper, and postexposure baked at 110° C. for 60 s. This was followed by a 30 secondpuddle development step with 0.26 N TMAH developer to resolve 0.190 μmline and space features.

Example 10 Elastic Modulus

Elastic modulus was measured for cured samples of each of the polymersof examples 4, 5, 6 and 7 using surface acoustics wave spectroscopy(SAWS). Films of the polymers were spin applied onto silicon wafers andthen post-applied baked at 110° C. for 1 min, exposed to 248 nm light,post-exposure baked at 110° C. for 1 min, and then thermally cured at400° C. The elastic modulus for the corresponding polymer filmsdescribed in examples 4, 5, 6 and 7 was 8.97, 8.8, 8.67, and 6.32 GParespectively.

Thus the embodiments of the present invention provide patternabledielectric materials, photo-sensitive formulations containingpatternable dielectric materials, methods of using photo-sensitiveformulations containing patternable dielectric materials in thefabrication of integrated circuits, and integrated circuit structurescomprising patternable dielectric materials. The methods according toembodiments of the present invention use less materials and require lesssteps than conventional methods.

The description of the embodiments of the present invention is givenabove for the understanding of the present invention. It will beunderstood that the invention is not limited to the particularembodiments described herein, but is capable of various modifications,rearrangements and substitutions as will now become apparent to thoseskilled in the art without departing from the scope of the invention.Therefore, it is intended that the following claims cover all suchmodifications and changes as fall within the true spirit and scope ofthe invention.

What is claimed is:
 1. A structure, comprising: a porous cross-linkedlayer of a silsesquioxane polymer on a substrate, said porouscross-linked layer comprises three monomers of the structural formulas(1), (7) and (3):

wherein R¹ is selected from the group consisting of linear alkyl,branched alkyl, cycloalkyl, aromatic, arene and ester moieties, eachcontaining 1 to 20 carbon atoms; wherein R³ is selected from the groupconsisting of linear alkyl, branched alkyl and cycloalkyl moieties, eachcontaining 1 to 20 carbon atoms; wherein m, q, and o, represent the molepercent (mol %) of repeating units with m+q+o equal to or greater thanabout 40 mol %; said porous cross-linked layer including an additivesilsesquioxane polymer of structure (5):

wherein R⁴ is selected from the group consisting of cycloalkyl and arylmoieties; and wherein s is an integer between about 10 and about 1000; atrench in said porous cross-linked layer; an electrically conductivematerial filling said trench and contacting said substrate in a bottomof said trench; an additional porous cross-linked layer of an additionalsilsesquioxane polymer directly on a top surface of said porouscross-linked layer; an additional trench in said additional porouscross-linked layer, a top of said trench open to a bottom of saidadditional trench; and said electrically conductive materialadditionally filling said additional trench.
 2. The structure of claim1, wherein said additional porous cross-linked layer comprises threemonomers of the structural formulas (1), (7) and (3)):

wherein R¹ is selected from the group consisting of linear alkyl,branched alkyl, cycloalkyl, aromatic, arene and ester moieties, eachcontaining 1 to 20 carbon atoms; wherein R³ is selected from the groupconsisting of linear alkyl, branched alkyl and cycloalkyl moieties, eachcontaining 1 to 20 carbon atoms; and wherein m, q, and o, represent themole percent (mol %) of repeating units with m+q+o equal to or greaterthan about 40 mol %.
 3. The structure of claim 1, wherein said porouscross-linked layer has a dielectric constant of 3.0 or less.
 4. Thestructure of claim 1, wherein said porous cross-linked layer consistsessentially of a cross-linked polymer of structural formulas (1), (7),and (3), R¹ is a methyl moiety and m is between about 40 mol % and about70 mol %, R³ is an ethyl moiety and o is between about 10 mol % andabout 30 mol %, and q is between about 5 mol % and about 15 mol %. 5.The structure of claim 1, wherein said additional porous cross-linkedlayer consists essentially of a cross-linked polymer of structuralformulas (1), (7), (3), R¹ is a methyl moiety and m is between about 40mol % and about 70 mol %, R³ is an ethyl moiety and o is between about10 mol % and about 30 mol %, and q is between about 5 mol % and about 15mol %.
 6. The structure of claim 1, wherein said additional porouscross-linked layer has a dielectric constant of about 3.0 or less. 7.The structure of claim 1, wherein said porous cross-linked layer has adielectric constant of 2.5 or less.
 8. The structure of claim 1, saidadditional porous cross-linked layer including: an additivesilsesquioxane polymer of structure (5):

wherein R⁴ is selected from the group consisting of cycloalkyl and arylmoieties; and wherein s is an integer between about 10 and about 1000.9. The structure of claim 1, wherein said additional porous cross-linkedlayer has a dielectric constant of 2.5 or less.
 10. A structurecomprising: a porous cross-linked layer of a silsesquioxane polymer on asubstrate, said porous cross-linked layer consists essentially of across-linked polymer of structural formulas (1), (7), and (3),

R¹ is a methyl moiety and m is between about 40 mol % and about 70 mol%, R³ is an ethyl moiety and o is between about 10 mol % and about 30mol %, and q is between about 5 mol % and about 15 mol %; a trench insaid porous cross-linked layer; an electrically conductive materialfilling said trench and contacting said substrate in a bottom of saidtrench; an additional porous cross-linked layer of an additionalsilsesquioxane polymer directly on a top surface of said porouscross-linked layer; an additional trench in said additional porouscross-linked layer, a top of said trench open to a bottom of saidadditional trench; and said electrically conductive materialadditionally filling said additional trench.